Hole drilling is the most widespread method for measuring residual stress. It is based on the pri... more Hole drilling is the most widespread method for measuring residual stress. It is based on the principle that drilling a hole in the material causes a local stress relaxation; the initial residual stress can be calculated bymeasuring strain in correspondence with each drill depth. Recently optical techniques were introduced to measure strain; in this case, the accuracy of the final results depends, among other factors, on the proper choice of the area of analysis. Deformations are in fact analyzed within an annulus determined by two parameters: the internal and the external radius. In this paper, the influence of the choice of the area of analysis was analysed. A known stress field was introduced on a Ti grade 5 sample and then the stress was measured in correspondence with different values of the internal and the external radius of analysis; results were finally compared with the expected theoretical value.
Ho/e drilling (HDM) is the most ividespread 1nethod for
measw·ing the residuai stress projìle. HD... more Ho/e drilling (HDM) is the most ividespread 1nethod for measw·ing the residuai stress projìle. HDM is based on the principle that a ho/e in the materiai causes stress relax:ation; stress jìeld around the ho/e changes so that the released strain can be measurnd in order to calculate initial residua! stress. Recently, the use of optical methods, as measurement tool for the strain jìeld genera/ed around the drilled ho/e, has been investigated in piace of the traditional strain gauge rosette technique. Optical methods have the advantage that guarantees ve1y high sensitivity, provides much more significant statistics, elimina/es error due to ho/e eccentricity, and reduces the cost in a single test. The accuracy of the jìnal results depends, among otherfactors, on the proper choice of the area of analysis. Defonnations detected by ESPI are in fact analysed 111ithin an annulus detennined by two parameters, that is to sey, the internal and the external radius. The choice of these parameters a.ffects the jìnal results in terms of measw·ed residuai stress. Results of this analysis are the object ofthis paper.
Hole drilling (HDM) is the most widespread method for measuring residual stress profile. HDM is b... more Hole drilling (HDM) is the most widespread method for measuring residual stress profile. HDM is based on the principle that a hole in the material causes a stress relaxation; stress field around the hole changes so that the released strain can be measured in order to calculate initial residual stress. Recently the use of optical methods as measurements tool of the strain field generated around the drilled hole has been investigated in place of the traditional strain gage rosette technique. Optical methods have the advantage to guarantee very high sensitivity, to provide a much more significant statistic, to eliminate error due to hole eccentricity and to reduce the cost of the single test. The accuracy of the final results depends, among other factors, on the exact knowledge of the geometrical parameters of the measuring system. The exact knowledge of the illumination and detection angles influences, in fact, the accuracy in the determination of the pixel size and of the sensitivity vector. The effect of an error in the measurement of the geometrical parameters on final residual stress results is presented in this paper besides some considerations about the accuracy in the zero position detection.
Innovative composite materials are frequently used in designing aerospace, naval and automotive c... more Innovative composite materials are frequently used in designing aerospace, naval and automotive components. In the typical structure of composites, multiple layers are stacked together with a particular sequence in order to give specific mechanical properties. Layers are organised with different angles, different sequences and different techno-logical process to obtain a new and innovative material. From the standpoint of engineering designer it is useful to consider the single layer of composite as macroscopi-cally homogeneous material. However, composites are non-homogeneous bodies. Moreover, layers are not often perfectly bonded together and delamination often occurs. Other violations of lamination theory hypotheses, such as plane stress and thin material, are not unusual and in many cases the transverse shear flexibility and the thickness-normal stiffness should be considered. Therefore the real behaviour of composite materials is quite different from the predictions coming from the traditional lamination theory. Due to the increasing structural performance required for innovative composites, the knowledge of mechanical properties for different loading cases is a fundamental source of concern. Experimental characterisation of mate-rials and structures in different environmental conditions is extremely important to understand the mechanical behav-iour of these new materials. The purpose of the present work is to characterise a composite material developed by Alenia Aeronautica for aerospace applications and produced by means of the resin film infusion process (RFI). Different tests have been carried out: tensile, open-hole and filled-hole tensile, compressive, open-hole and filled-hole compressive. The experimental campaign has the aim to define mechanical characteristics of this RFI composite material in different conditions: environmental tempera-ture, Hot/Wet and Cold.
Most of the manufacturing processes generate residual stresses inside materials and components. S... more Most of the manufacturing processes generate residual stresses inside materials and components. Stress relief heat treatments can be used to reduce the residual stresses magnitude. Uniformly heating a structure to a sufficiently high temperature, and then uniformly cooling it, allows relaxing residual stresses. This process generally involves the entire component (that should be put in a large furnace), and gives results that could be controversial if correlated to the mechanical response of material. In this paper the study is focused on the possibility to use a high power laser source to locally relieve residual stresses, with the advantage of calibrating and bordering the relieving process just on the residual stress affected area. An experimental set up is carried out on aluminum specimen and the preliminary results are reported in this paper.
Hole drilling (HDM) is the most widespread approach for measuring residual stress profile. Many i... more Hole drilling (HDM) is the most widespread approach for measuring residual stress profile. Many improvements were introduced along the years. Recently, research papers investigated the feasibility of using optical systems to replace strain gage rosette as measurement tool of the strain field generated by the drilled hole. Generally, the accuracy of the measurement is influenced by the proper choice of the experimental and analysis parameters. In this paper the effects of the choice of a proper analysis area are shown. Furthermore the influence of the drilling rotation speed of the cutter used for drilling the hole is considered. Experimental tests were performed on a Ti6Al4V specimen loaded in a four point bending frame. Results obtained for different part of the analysis area and at different speeds ranging in 5000 ÷ 50000 rpm were compared with the theoretical expected value.
Residual stresses occur in many manufactured structures and components. Great number of investiga... more Residual stresses occur in many manufactured structures and components. Great number of investigations have been carried out to study this phenomenon. Over the years, different techniques have been developed to measure residual stresses; nowadays the combination of Hole Drilling method (HD) with Electronic Speckle Pattern Interferometry (ESPI) has encountered great interest. The use of a high sensitivity optical technique instead of the strain gage rosette has the advantage to provide full field information without any contact with the sample by consequently reducing the cost and the time required for the measurement. The accuracy of the measurement, however, is influenced by the proper choice of several parameters: geometrical, analysis and experimental. In this paper, in particular, the effects of some of those parameters are investigated: misknowledgement in illumination and detection angles, the influence of the relative angle between the sensitivity vector of the system and the principal stress directions, the extension of the area of analysis and the adopted drilling rotation speed. In conclusion indications are provided to the scope of optimizing the measurement process together with the identification of the major sources of errors that can arise during the measuring and the analysis stages.
Hole drilling is the most widespread method for measuring residual stress. This method is based o... more Hole drilling is the most widespread method for measuring residual stress. This method is based on the principle that drilling a hole in a material causes stress relaxation; by measuring the resulting strain it is possible to calculate the initial residual stress. Recently optical systems were introduced to replace strain gage rosette since they can provide full field measurements with high sensitivity. When using ESPI technique, the analysis area, that is to say, the portion of the image which must be used for measuring strain is defined by the operator. Proper choice of this area can be affected by many factors. In this paper, in particular, the influence of drilling rotation speed is investigated. To this scope measurements at three different speeds were carried out and for each speed the temperature field around the hole was measured by using a thermocamera.
Hole drilling (HDM) is the most widespread approach for measuring residual stress profile and it ... more Hole drilling (HDM) is the most widespread approach for measuring residual stress profile and it is, at the moment, the only technique to be ruled by a standard. Many improvements were introduced along the years and recently research papers investigated the feasibility to use optical systems to replace strain gage rosette as measurement tool of the strain field generated by the drilled hole. Generally speaking, the accuracy of the measurement is influenced by the proper choice of the experimental and analysis parameters. In this paper the effects of the choice of a proper analysis area, to be intended as the portion of the image captured by the CCD camera whose data are used to calculate the strain values, are shown. Furthermore the influence of the drilling rotation speed of the cutter used for drilling the hole is investigated. Experimental tests were performed on a Ti6Al4V specimen loaded in a four point bending frame up to 50% of the yield strength. Drilling speeds ranging between 5000 ÷ 50000 rpm were investigated by using an electronically controlled mill. Results obtained at different speeds and for different locations of the analysis area were compared with the theoretical expected value and with results from a numerical model implemented in ANSYS®.
Stress relief heat treatment is used to reduce the residual stresses in a structure produced from... more Stress relief heat treatment is used to reduce the residual stresses in a structure produced from manufacturing processes. There are many sources of residual stresses, and in particular those due to welding process could be of a magnitude roughly equal to the yield strength of the base material. Uniformly heating a structure to a sufficiently high temperature, but below the lower transformation temperature range, and then uniformly cooling it, can relax these residual stresses. In this paper the attention is focused on the possibility to use a high power laser source that local heats a component in order to relieve the residual stresses. An experimental set up is carried out on aluminum specimen and the preliminary results reported in this paper.
This paper describes the process of mechanical characterization of orthotropic materials. An hybr... more This paper describes the process of mechanical characterization of orthotropic materials. An hybrid approach based on the combination of phase-shifting electronic speckle pattern interferometry (PS-ESPI) and finite element analysis is utilized. Three-point-bending experimental tests are carried out. The difference between displacement values measured with ESPI and their counterpart predicted by FEM analysis is minimized in order to find the values of the unknown elastic constants.
In this paper the crack propagation process was monitored by two different experimental technique... more In this paper the crack propagation process was monitored by two different experimental techniques. Acoustic emissions sensors were placed on the sample in order to monitor the evolution of the acoustical events during the test; at the same time the change in temperature was monitored by thermography. Test were run on aluminum samples (Al 5068). Specimens were previously cracked, by cutting notches having known sizes and geometry. Successively, X-Ray diffractometry analysis were performed in order to establish the given initial stress state of each sample. Specimen were then subjected to mechanical tests. During these tests the crack propagation was continuously monitored and recorded by both techniques. Data obtained, in terms of number of hits, amplitude signals and maps’ temperature, were critically compared in order to assess the capability of each technique in following the evolution of the damage process.
The effect, on the residual stress measurement accuracy, of the drilling speed of the end-mill du... more The effect, on the residual stress measurement accuracy, of the drilling speed of the end-mill during the hole-drilling measurements was evaluated in Ti6Al4V. In spite of the well-known consideration that the highest achievable speed should be used during hole drilling, very few experimental works exist analyzing the effects of using lower velocities. Hole-drilling experiments were performed in this study by measuring the released strain by electronic speckle pattern interferometry. A known stress state was generated by loading the sample in a four point bending frame up to 50% of the yield strength. Drilling speed ranging in 5000 ÷ 50000 rpm was investigated by using an electronically controlled mill. The expected stress field, evaluated by a numerical model in ANSYS®, was compared with the measured one at different drilling speeds.
This paper deals with the study of acoustic emissions (AE) from aluminum Al5068 specimen during l... more This paper deals with the study of acoustic emissions (AE) from aluminum Al5068 specimen during local annealing process by a laser diode source. The heating cycle, obtained by irradiating the surface of the specimen, causes a change in the local stress state which can be studied by X-Ray diffractometry; at the same time acoustic emissions can be recorded as a consequence of residual stress relieving. This hybrid approach provides evidence of the presence of a correlation between stress relieving and the number of signals of acoustic emissions recorded during the heating and the cooling stages. Annealing cycle was repeated several times and acoustic emissions were detected during each cycle; the amount of residual stresses along the longitudinal direction was measured at the end of each cycle as well. The number of acoustic signals exhibits the typical behavior due to the Kaiser effect while residual stresses show a quite regular decrease from cycle to cycle. Mechanical tensile tests have also been performed on the same specimen tested at four different loads. In this case too, experimental results show evidence of Kaiser effect, however a steeper reduction of the number of signals is observed with respect to the thermal tests.
In the last decades wood has assumed an increasing relevance in building engineering both due to ... more In the last decades wood has assumed an increasing relevance in building engineering both due to new technologies in wood production and manufacturing, such as computer-aided optimization of log sawing, automated lumber grading etc., and to the development of the green building. Fibrous structure of the wood makes it an orthotropic material so that it becomes important to perform a measurement, which allows to fully characterize the orthotropic properties of the specimen. Hybrid numerical-experimental techniques can be used in order to accurately determine the Young modulus and the Poisson coefficient of the material. In this paper a hybrid procedure based on an optical technique (Electronic Speckle Pattern Interferometry, ESPI) and a numerical optimization algorithm was implemented in order to characterize a specimen of a laminated soft wood. Three-point-bending experimental tests were carried out and the material properties were iteratively modified in order to minimize the difference between the experimentally measured displacement field and the corresponding displacement field obtained by FEM calculations.
Hole drilling is the most widespread method for measuring residual stress. It is based on the pri... more Hole drilling is the most widespread method for measuring residual stress. It is based on the principle that drilling a hole in the material causes a local stress relaxation; the initial residual stress can be calculated bymeasuring strain in correspondence with each drill depth. Recently optical techniques were introduced to measure strain; in this case, the accuracy of the final results depends, among other factors, on the proper choice of the area of analysis. Deformations are in fact analyzed within an annulus determined by two parameters: the internal and the external radius. In this paper, the influence of the choice of the area of analysis was analysed. A known stress field was introduced on a Ti grade 5 sample and then the stress was measured in correspondence with different values of the internal and the external radius of analysis; results were finally compared with the expected theoretical value.
Ho/e drilling (HDM) is the most ividespread 1nethod for
measw·ing the residuai stress projìle. HD... more Ho/e drilling (HDM) is the most ividespread 1nethod for measw·ing the residuai stress projìle. HDM is based on the principle that a ho/e in the materiai causes stress relax:ation; stress jìeld around the ho/e changes so that the released strain can be measurnd in order to calculate initial residua! stress. Recently, the use of optical methods, as measurement tool for the strain jìeld genera/ed around the drilled ho/e, has been investigated in piace of the traditional strain gauge rosette technique. Optical methods have the advantage that guarantees ve1y high sensitivity, provides much more significant statistics, elimina/es error due to ho/e eccentricity, and reduces the cost in a single test. The accuracy of the jìnal results depends, among otherfactors, on the proper choice of the area of analysis. Defonnations detected by ESPI are in fact analysed 111ithin an annulus detennined by two parameters, that is to sey, the internal and the external radius. The choice of these parameters a.ffects the jìnal results in terms of measw·ed residuai stress. Results of this analysis are the object ofthis paper.
Hole drilling (HDM) is the most widespread method for measuring residual stress profile. HDM is b... more Hole drilling (HDM) is the most widespread method for measuring residual stress profile. HDM is based on the principle that a hole in the material causes a stress relaxation; stress field around the hole changes so that the released strain can be measured in order to calculate initial residual stress. Recently the use of optical methods as measurements tool of the strain field generated around the drilled hole has been investigated in place of the traditional strain gage rosette technique. Optical methods have the advantage to guarantee very high sensitivity, to provide a much more significant statistic, to eliminate error due to hole eccentricity and to reduce the cost of the single test. The accuracy of the final results depends, among other factors, on the exact knowledge of the geometrical parameters of the measuring system. The exact knowledge of the illumination and detection angles influences, in fact, the accuracy in the determination of the pixel size and of the sensitivity vector. The effect of an error in the measurement of the geometrical parameters on final residual stress results is presented in this paper besides some considerations about the accuracy in the zero position detection.
Innovative composite materials are frequently used in designing aerospace, naval and automotive c... more Innovative composite materials are frequently used in designing aerospace, naval and automotive components. In the typical structure of composites, multiple layers are stacked together with a particular sequence in order to give specific mechanical properties. Layers are organised with different angles, different sequences and different techno-logical process to obtain a new and innovative material. From the standpoint of engineering designer it is useful to consider the single layer of composite as macroscopi-cally homogeneous material. However, composites are non-homogeneous bodies. Moreover, layers are not often perfectly bonded together and delamination often occurs. Other violations of lamination theory hypotheses, such as plane stress and thin material, are not unusual and in many cases the transverse shear flexibility and the thickness-normal stiffness should be considered. Therefore the real behaviour of composite materials is quite different from the predictions coming from the traditional lamination theory. Due to the increasing structural performance required for innovative composites, the knowledge of mechanical properties for different loading cases is a fundamental source of concern. Experimental characterisation of mate-rials and structures in different environmental conditions is extremely important to understand the mechanical behav-iour of these new materials. The purpose of the present work is to characterise a composite material developed by Alenia Aeronautica for aerospace applications and produced by means of the resin film infusion process (RFI). Different tests have been carried out: tensile, open-hole and filled-hole tensile, compressive, open-hole and filled-hole compressive. The experimental campaign has the aim to define mechanical characteristics of this RFI composite material in different conditions: environmental tempera-ture, Hot/Wet and Cold.
Most of the manufacturing processes generate residual stresses inside materials and components. S... more Most of the manufacturing processes generate residual stresses inside materials and components. Stress relief heat treatments can be used to reduce the residual stresses magnitude. Uniformly heating a structure to a sufficiently high temperature, and then uniformly cooling it, allows relaxing residual stresses. This process generally involves the entire component (that should be put in a large furnace), and gives results that could be controversial if correlated to the mechanical response of material. In this paper the study is focused on the possibility to use a high power laser source to locally relieve residual stresses, with the advantage of calibrating and bordering the relieving process just on the residual stress affected area. An experimental set up is carried out on aluminum specimen and the preliminary results are reported in this paper.
Hole drilling (HDM) is the most widespread approach for measuring residual stress profile. Many i... more Hole drilling (HDM) is the most widespread approach for measuring residual stress profile. Many improvements were introduced along the years. Recently, research papers investigated the feasibility of using optical systems to replace strain gage rosette as measurement tool of the strain field generated by the drilled hole. Generally, the accuracy of the measurement is influenced by the proper choice of the experimental and analysis parameters. In this paper the effects of the choice of a proper analysis area are shown. Furthermore the influence of the drilling rotation speed of the cutter used for drilling the hole is considered. Experimental tests were performed on a Ti6Al4V specimen loaded in a four point bending frame. Results obtained for different part of the analysis area and at different speeds ranging in 5000 ÷ 50000 rpm were compared with the theoretical expected value.
Residual stresses occur in many manufactured structures and components. Great number of investiga... more Residual stresses occur in many manufactured structures and components. Great number of investigations have been carried out to study this phenomenon. Over the years, different techniques have been developed to measure residual stresses; nowadays the combination of Hole Drilling method (HD) with Electronic Speckle Pattern Interferometry (ESPI) has encountered great interest. The use of a high sensitivity optical technique instead of the strain gage rosette has the advantage to provide full field information without any contact with the sample by consequently reducing the cost and the time required for the measurement. The accuracy of the measurement, however, is influenced by the proper choice of several parameters: geometrical, analysis and experimental. In this paper, in particular, the effects of some of those parameters are investigated: misknowledgement in illumination and detection angles, the influence of the relative angle between the sensitivity vector of the system and the principal stress directions, the extension of the area of analysis and the adopted drilling rotation speed. In conclusion indications are provided to the scope of optimizing the measurement process together with the identification of the major sources of errors that can arise during the measuring and the analysis stages.
Hole drilling is the most widespread method for measuring residual stress. This method is based o... more Hole drilling is the most widespread method for measuring residual stress. This method is based on the principle that drilling a hole in a material causes stress relaxation; by measuring the resulting strain it is possible to calculate the initial residual stress. Recently optical systems were introduced to replace strain gage rosette since they can provide full field measurements with high sensitivity. When using ESPI technique, the analysis area, that is to say, the portion of the image which must be used for measuring strain is defined by the operator. Proper choice of this area can be affected by many factors. In this paper, in particular, the influence of drilling rotation speed is investigated. To this scope measurements at three different speeds were carried out and for each speed the temperature field around the hole was measured by using a thermocamera.
Hole drilling (HDM) is the most widespread approach for measuring residual stress profile and it ... more Hole drilling (HDM) is the most widespread approach for measuring residual stress profile and it is, at the moment, the only technique to be ruled by a standard. Many improvements were introduced along the years and recently research papers investigated the feasibility to use optical systems to replace strain gage rosette as measurement tool of the strain field generated by the drilled hole. Generally speaking, the accuracy of the measurement is influenced by the proper choice of the experimental and analysis parameters. In this paper the effects of the choice of a proper analysis area, to be intended as the portion of the image captured by the CCD camera whose data are used to calculate the strain values, are shown. Furthermore the influence of the drilling rotation speed of the cutter used for drilling the hole is investigated. Experimental tests were performed on a Ti6Al4V specimen loaded in a four point bending frame up to 50% of the yield strength. Drilling speeds ranging between 5000 ÷ 50000 rpm were investigated by using an electronically controlled mill. Results obtained at different speeds and for different locations of the analysis area were compared with the theoretical expected value and with results from a numerical model implemented in ANSYS®.
Stress relief heat treatment is used to reduce the residual stresses in a structure produced from... more Stress relief heat treatment is used to reduce the residual stresses in a structure produced from manufacturing processes. There are many sources of residual stresses, and in particular those due to welding process could be of a magnitude roughly equal to the yield strength of the base material. Uniformly heating a structure to a sufficiently high temperature, but below the lower transformation temperature range, and then uniformly cooling it, can relax these residual stresses. In this paper the attention is focused on the possibility to use a high power laser source that local heats a component in order to relieve the residual stresses. An experimental set up is carried out on aluminum specimen and the preliminary results reported in this paper.
This paper describes the process of mechanical characterization of orthotropic materials. An hybr... more This paper describes the process of mechanical characterization of orthotropic materials. An hybrid approach based on the combination of phase-shifting electronic speckle pattern interferometry (PS-ESPI) and finite element analysis is utilized. Three-point-bending experimental tests are carried out. The difference between displacement values measured with ESPI and their counterpart predicted by FEM analysis is minimized in order to find the values of the unknown elastic constants.
In this paper the crack propagation process was monitored by two different experimental technique... more In this paper the crack propagation process was monitored by two different experimental techniques. Acoustic emissions sensors were placed on the sample in order to monitor the evolution of the acoustical events during the test; at the same time the change in temperature was monitored by thermography. Test were run on aluminum samples (Al 5068). Specimens were previously cracked, by cutting notches having known sizes and geometry. Successively, X-Ray diffractometry analysis were performed in order to establish the given initial stress state of each sample. Specimen were then subjected to mechanical tests. During these tests the crack propagation was continuously monitored and recorded by both techniques. Data obtained, in terms of number of hits, amplitude signals and maps’ temperature, were critically compared in order to assess the capability of each technique in following the evolution of the damage process.
The effect, on the residual stress measurement accuracy, of the drilling speed of the end-mill du... more The effect, on the residual stress measurement accuracy, of the drilling speed of the end-mill during the hole-drilling measurements was evaluated in Ti6Al4V. In spite of the well-known consideration that the highest achievable speed should be used during hole drilling, very few experimental works exist analyzing the effects of using lower velocities. Hole-drilling experiments were performed in this study by measuring the released strain by electronic speckle pattern interferometry. A known stress state was generated by loading the sample in a four point bending frame up to 50% of the yield strength. Drilling speed ranging in 5000 ÷ 50000 rpm was investigated by using an electronically controlled mill. The expected stress field, evaluated by a numerical model in ANSYS®, was compared with the measured one at different drilling speeds.
This paper deals with the study of acoustic emissions (AE) from aluminum Al5068 specimen during l... more This paper deals with the study of acoustic emissions (AE) from aluminum Al5068 specimen during local annealing process by a laser diode source. The heating cycle, obtained by irradiating the surface of the specimen, causes a change in the local stress state which can be studied by X-Ray diffractometry; at the same time acoustic emissions can be recorded as a consequence of residual stress relieving. This hybrid approach provides evidence of the presence of a correlation between stress relieving and the number of signals of acoustic emissions recorded during the heating and the cooling stages. Annealing cycle was repeated several times and acoustic emissions were detected during each cycle; the amount of residual stresses along the longitudinal direction was measured at the end of each cycle as well. The number of acoustic signals exhibits the typical behavior due to the Kaiser effect while residual stresses show a quite regular decrease from cycle to cycle. Mechanical tensile tests have also been performed on the same specimen tested at four different loads. In this case too, experimental results show evidence of Kaiser effect, however a steeper reduction of the number of signals is observed with respect to the thermal tests.
In the last decades wood has assumed an increasing relevance in building engineering both due to ... more In the last decades wood has assumed an increasing relevance in building engineering both due to new technologies in wood production and manufacturing, such as computer-aided optimization of log sawing, automated lumber grading etc., and to the development of the green building. Fibrous structure of the wood makes it an orthotropic material so that it becomes important to perform a measurement, which allows to fully characterize the orthotropic properties of the specimen. Hybrid numerical-experimental techniques can be used in order to accurately determine the Young modulus and the Poisson coefficient of the material. In this paper a hybrid procedure based on an optical technique (Electronic Speckle Pattern Interferometry, ESPI) and a numerical optimization algorithm was implemented in order to characterize a specimen of a laminated soft wood. Three-point-bending experimental tests were carried out and the material properties were iteratively modified in order to minimize the difference between the experimentally measured displacement field and the corresponding displacement field obtained by FEM calculations.
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Papers by Claudia Barile
by two parameters: the internal and the external radius. In this paper, the influence of the choice of the area of analysis was analysed.
A known stress field was introduced on a Ti grade 5 sample and then the stress was measured in correspondence with different values of the internal and the external radius of analysis; results were finally compared with the expected theoretical value.
measw·ing the residuai stress projìle. HDM is based on the
principle that a ho/e in the materiai causes stress relax:ation;
stress jìeld around the ho/e changes so that the released
strain can be measurnd in order to calculate initial residua!
stress. Recently, the use of optical methods, as measurement
tool for the strain jìeld genera/ed around the drilled ho/e, has
been investigated in piace of the traditional strain gauge
rosette technique. Optical methods have the advantage that
guarantees ve1y high sensitivity, provides much more significant statistics, elimina/es error due to ho/e eccentricity, and reduces the cost in a single test. The accuracy of the jìnal
results depends, among otherfactors, on the proper choice of
the area of analysis. Defonnations detected by ESPI are in
fact analysed 111ithin an annulus detennined by two parameters, that is to sey, the internal and the external radius. The choice of these parameters a.ffects the jìnal results in terms of measw·ed residuai stress. Results of this analysis are the object ofthis paper.
From the standpoint of engineering designer it is useful to consider the single layer of composite as macroscopi-cally homogeneous material. However, composites are non-homogeneous bodies. Moreover, layers are not often perfectly bonded together and delamination often occurs. Other violations of lamination theory hypotheses, such as plane stress and thin material, are not unusual and in many cases the transverse shear flexibility and the thickness-normal stiffness should be considered.
Therefore the real behaviour of composite materials is quite different from the predictions coming from the traditional lamination theory.
Due to the increasing structural performance required for innovative composites, the knowledge of mechanical properties for different loading cases is a fundamental source of concern. Experimental characterisation of mate-rials and structures in different environmental conditions is extremely important to understand the mechanical behav-iour of these new materials.
The purpose of the present work is to characterise a composite material developed by Alenia Aeronautica for aerospace applications and produced by means of the resin film infusion process (RFI).
Different tests have been carried out: tensile, open-hole and filled-hole tensile, compressive, open-hole and filled-hole compressive. The experimental campaign has the aim to define mechanical characteristics of this RFI composite material in different conditions: environmental tempera-ture, Hot/Wet and Cold.
In this paper the study is focused on the possibility to use a high power laser source to locally relieve residual stresses, with the advantage of calibrating and bordering the relieving process just on the residual stress affected area. An experimental set up is carried out on aluminum specimen and the preliminary results are reported in this paper.
by measuring the resulting strain it is possible to calculate the initial residual stress. Recently optical systems were introduced to replace strain gage rosette since they can provide
full field measurements with high sensitivity. When using ESPI technique, the analysis area, that is to say, the portion of the image which must be used for measuring strain is defined
by the operator. Proper choice of this area can be affected by many factors. In this paper, in particular, the influence of drilling rotation speed is investigated. To this scope measurements at three different speeds were carried out and for each speed the temperature field around the hole was measured by using a thermocamera.
combination of phase-shifting electronic speckle pattern interferometry (PS-ESPI) and finite element analysis is utilized. Three-point-bending experimental tests are carried out. The difference between displacement values measured with ESPI and their counterpart predicted by FEM analysis is minimized in order to find the values of the unknown elastic constants.
measurements was evaluated in Ti6Al4V. In spite of the well-known consideration that the highest achievable speed should
be used during hole drilling, very few experimental works exist analyzing the effects of using lower velocities. Hole-drilling
experiments were performed in this study by measuring the released strain by electronic speckle pattern interferometry. A
known stress state was generated by loading the sample in a four point bending frame up to 50% of the yield strength.
Drilling speed ranging in 5000 ÷ 50000 rpm was investigated by using an electronically controlled mill. The expected stress
field, evaluated by a numerical model in ANSYS®, was compared with the measured one at different drilling speeds.
by a laser diode source. The heating cycle, obtained by irradiating the surface of the specimen, causes a change in the local stress state which can be studied by X-Ray diffractometry; at the same time acoustic emissions can be recorded as a
consequence of residual stress relieving.
This hybrid approach provides evidence of the presence of a correlation between stress relieving and the number of signals of acoustic emissions recorded during the heating and the cooling stages. Annealing cycle was repeated several times and
acoustic emissions were detected during each cycle; the amount of residual stresses along the longitudinal direction was measured at the end of each cycle as well. The number of acoustic signals exhibits the typical behavior due to the Kaiser
effect while residual stresses show a quite regular decrease from cycle to cycle. Mechanical tensile tests have also been
performed on the same specimen tested at four different loads. In this case too, experimental results show evidence of Kaiser effect, however a steeper reduction of the number of signals is observed with respect to the thermal tests.
production and manufacturing, such as computer-aided optimization of log sawing, automated lumber grading etc., and to
the development of the green building. Fibrous structure of the wood makes it an orthotropic material so that it becomes
important to perform a measurement, which allows to fully characterize the orthotropic properties of the specimen. Hybrid
numerical-experimental techniques can be used in order to accurately determine the Young modulus and the Poisson
coefficient of the material.
In this paper a hybrid procedure based on an optical technique (Electronic Speckle Pattern Interferometry, ESPI) and a
numerical optimization algorithm was implemented in order to characterize a specimen of a laminated soft wood.
Three-point-bending experimental tests were carried out and the material properties were iteratively modified in order to
minimize the difference between the experimentally measured displacement field and the corresponding displacement field
obtained by FEM calculations.
by two parameters: the internal and the external radius. In this paper, the influence of the choice of the area of analysis was analysed.
A known stress field was introduced on a Ti grade 5 sample and then the stress was measured in correspondence with different values of the internal and the external radius of analysis; results were finally compared with the expected theoretical value.
measw·ing the residuai stress projìle. HDM is based on the
principle that a ho/e in the materiai causes stress relax:ation;
stress jìeld around the ho/e changes so that the released
strain can be measurnd in order to calculate initial residua!
stress. Recently, the use of optical methods, as measurement
tool for the strain jìeld genera/ed around the drilled ho/e, has
been investigated in piace of the traditional strain gauge
rosette technique. Optical methods have the advantage that
guarantees ve1y high sensitivity, provides much more significant statistics, elimina/es error due to ho/e eccentricity, and reduces the cost in a single test. The accuracy of the jìnal
results depends, among otherfactors, on the proper choice of
the area of analysis. Defonnations detected by ESPI are in
fact analysed 111ithin an annulus detennined by two parameters, that is to sey, the internal and the external radius. The choice of these parameters a.ffects the jìnal results in terms of measw·ed residuai stress. Results of this analysis are the object ofthis paper.
From the standpoint of engineering designer it is useful to consider the single layer of composite as macroscopi-cally homogeneous material. However, composites are non-homogeneous bodies. Moreover, layers are not often perfectly bonded together and delamination often occurs. Other violations of lamination theory hypotheses, such as plane stress and thin material, are not unusual and in many cases the transverse shear flexibility and the thickness-normal stiffness should be considered.
Therefore the real behaviour of composite materials is quite different from the predictions coming from the traditional lamination theory.
Due to the increasing structural performance required for innovative composites, the knowledge of mechanical properties for different loading cases is a fundamental source of concern. Experimental characterisation of mate-rials and structures in different environmental conditions is extremely important to understand the mechanical behav-iour of these new materials.
The purpose of the present work is to characterise a composite material developed by Alenia Aeronautica for aerospace applications and produced by means of the resin film infusion process (RFI).
Different tests have been carried out: tensile, open-hole and filled-hole tensile, compressive, open-hole and filled-hole compressive. The experimental campaign has the aim to define mechanical characteristics of this RFI composite material in different conditions: environmental tempera-ture, Hot/Wet and Cold.
In this paper the study is focused on the possibility to use a high power laser source to locally relieve residual stresses, with the advantage of calibrating and bordering the relieving process just on the residual stress affected area. An experimental set up is carried out on aluminum specimen and the preliminary results are reported in this paper.
by measuring the resulting strain it is possible to calculate the initial residual stress. Recently optical systems were introduced to replace strain gage rosette since they can provide
full field measurements with high sensitivity. When using ESPI technique, the analysis area, that is to say, the portion of the image which must be used for measuring strain is defined
by the operator. Proper choice of this area can be affected by many factors. In this paper, in particular, the influence of drilling rotation speed is investigated. To this scope measurements at three different speeds were carried out and for each speed the temperature field around the hole was measured by using a thermocamera.
combination of phase-shifting electronic speckle pattern interferometry (PS-ESPI) and finite element analysis is utilized. Three-point-bending experimental tests are carried out. The difference between displacement values measured with ESPI and their counterpart predicted by FEM analysis is minimized in order to find the values of the unknown elastic constants.
measurements was evaluated in Ti6Al4V. In spite of the well-known consideration that the highest achievable speed should
be used during hole drilling, very few experimental works exist analyzing the effects of using lower velocities. Hole-drilling
experiments were performed in this study by measuring the released strain by electronic speckle pattern interferometry. A
known stress state was generated by loading the sample in a four point bending frame up to 50% of the yield strength.
Drilling speed ranging in 5000 ÷ 50000 rpm was investigated by using an electronically controlled mill. The expected stress
field, evaluated by a numerical model in ANSYS®, was compared with the measured one at different drilling speeds.
by a laser diode source. The heating cycle, obtained by irradiating the surface of the specimen, causes a change in the local stress state which can be studied by X-Ray diffractometry; at the same time acoustic emissions can be recorded as a
consequence of residual stress relieving.
This hybrid approach provides evidence of the presence of a correlation between stress relieving and the number of signals of acoustic emissions recorded during the heating and the cooling stages. Annealing cycle was repeated several times and
acoustic emissions were detected during each cycle; the amount of residual stresses along the longitudinal direction was measured at the end of each cycle as well. The number of acoustic signals exhibits the typical behavior due to the Kaiser
effect while residual stresses show a quite regular decrease from cycle to cycle. Mechanical tensile tests have also been
performed on the same specimen tested at four different loads. In this case too, experimental results show evidence of Kaiser effect, however a steeper reduction of the number of signals is observed with respect to the thermal tests.
production and manufacturing, such as computer-aided optimization of log sawing, automated lumber grading etc., and to
the development of the green building. Fibrous structure of the wood makes it an orthotropic material so that it becomes
important to perform a measurement, which allows to fully characterize the orthotropic properties of the specimen. Hybrid
numerical-experimental techniques can be used in order to accurately determine the Young modulus and the Poisson
coefficient of the material.
In this paper a hybrid procedure based on an optical technique (Electronic Speckle Pattern Interferometry, ESPI) and a
numerical optimization algorithm was implemented in order to characterize a specimen of a laminated soft wood.
Three-point-bending experimental tests were carried out and the material properties were iteratively modified in order to
minimize the difference between the experimentally measured displacement field and the corresponding displacement field
obtained by FEM calculations.